Fluid bed granulation apparatus

ABSTRACT

A nozzle for distributor devices of granule&#39;s growth liquid substance in fluid bed granulators, is distinguished by the fact that it comprises a duct ( 2 ) having, at one end, at least one inlet opening ( 3 ) for a flow (F) of a chosen granule&#39;s growth liquid substance, and, at the other end, a supply opening ( 5 ) for such substance, a gaseous flow distributor ( 6 ) externally associated to the duct ( 2 ) in predetermined spaced relationship from the supply opening ( 5 ) and in fluid communication with the inside of the duct ( 2 ), and emulsifying means ( 8 ) associated to the inlet opening ( 3 ) and the distributor ( 6 ) to obtain, inside the duct ( 2 ), an emulsion of the gaseous flow in the growth liquid substance.

FIELD OF APPLICATION

In its most general aspect, the present invention relates to anapparatus for fluid bed granulation processes where granules of a chosensubstance are obtained through continuous growth (of both volume andmass) of granules and seeds of that substance suspended in a fluid bed,by means of a suitable growth substance in the fluid state, continuouslyfed in said fluid bed.

Particularly, this invention concerns a granulation apparatus comprisinga container, wherein a fluid bed of seeds and granules of the chosensubstance to be granulated is obtained, a device for feedingcontinuously said seeds in said fluid bed, a fluidification and supportsystem of the fluid bed and at least a distributor of a flow of thegrowth liquid, comprising a plurality of nozzles for supplying saidliquid.

More particularly, this invention relates to a supplying nozzle for thegranule-growth liquid substance, usable for granulation apparatus of theabove kind.

In the following description and attached claims, such apparatus will begenerally addressed as granulator, while the expression: “granule's seedof a chosen substance”, is generally meant to indicate particles of thesubstance to be granulated having dimensions equal or less than about1.5 mm in diameter. Furthermore, to simplify, the term “seeds” will beused to indicate the granule's seeds.

PRIOR ART

It's known that to reach a good granulation outcome (prearrangedgranule's dimension, shape and mass) with a fluid bed process of theabove type, a good “wetting” of both the seeds and the growing granulesby the growth liquid is required. And, to this end, the growth liquidmust be fed to the fluid bed in the form of the least possible droplets,certainly less than the seeds and the growing granules, which saiddroplets are to get in touch with. That's to allow, as for example withthe urea, the evaporation of water or different solvent contained in thegrowth liquid (solution of urea), in the fastest and most completepossible way, so as to obtain a high purity final product (granules).

From this point of view, the dimension of the growth liquid droplets isso crucial that it's very advantageous, if not necessary, to feed saidgrowth liquid in the so-called “atomized” form. In this condition,actually, the growth liquid is able to get in touch one by one with allthe seeds or granules suspended in the fluid bed, and to wet evenly andin an optimal way their whole surface.

In order to atomize the growth liquid, the prior art granulators and,more specifically, their growth liquid supplying devices, make use ofspecific atomizing nozzles fed with said liquid and at the same timewith large amounts of air (or other suitable gas) at high speed. Suchspeed is, for example, when considering urea granulation, comprisedbetween 150 m/s and 300 m/s, with an air/liquid substance ratiotypically comprised between 0.4 and 0.5 (that is 400-500 Kg of airagainst 1000 Kg of liquid substance).

But, although largely used and being advantageous under some points ofview, the use of the atomizing nozzle of the above mentioned type causesknown drawbacks not yet overcame in the fluid bed granulation processesof the prior art. Actually, the need to work with large amounts of air(or other gas) at high speed prevents a control of the granule growthinside the fluid bed and, consequently, leads to the inability tocontrol the final product granulometry between predetermined limitedvalues. This entails expensive classification and screening operationsof the produced granules, the recovery of granules of unacceptable size(too big or too little), and their recycle upstream to the granulationprocess.

Furthermore, feeding large amounts of atomizing air (or other suitablegas) at high pressure to obtain the above-mentioned speed gives rise tosuch extremely high consumption of energy that the production costs ofthe granules are substantially affected.

SUMMARY OF THE INVENTION

The problem underlying the present invention is to devise and to makeavailable a nozzle for distribution devices of growth liquid substancein fluid bed granulators, having structural and functional features inorder to obtain the following goals.

First, said growth liquid substance should be made available in asuitable form to obtain a good granulation product by using amounts ofair (or other suitable gas) much reduced with respect to what iscurrently possible. Second, said growth liquid substance should besupplied with speeds so low as to overcome all the cited drawbackslinked to the prior art.

The idea of solution underlying the present invention is to makeavailable a nozzle able to carry out a dispersion of air (or othersuitable gas) into the growth liquid substance, which is to say anemulsion of the gaseous phase into the liquid phase. It should bepointed out that this is in clear contradiction with the teaching of theprior art that makes use of atomizing nozzles to disperse the growthliquid substance into the gaseous flow.

The above technical problem is thereby solved according to theinvention, by a nozzle of the above-mentioned type, characterized by thefact that it comprises a duct having, at one end, at least one inletopening for a flow of a chosen granule's growth liquid substance, and,at the other end, a supply opening for such substance, a gaseous flowdistributor externally associated to said duct in predetermined spacedrelationship from said supply opening and in fluid communication withthe inside of said duct, and emulsifying means associated to said inletopening and said distributor to obtain, inside said duct, an emulsion ofsaid gaseous flow in said growth liquid substance.

Preferably, the emulsifying means include a swirling device locatedinside the duct between said at least one input opening and saiddistributor, the swirling device being able to impart a helical motionto an axial flow of the growth liquid substance inside the duct.

A first important advantage achieved by the present invention is thefact that the possibility to obtain, through the nozzle according to theinvention, a gas-in-liquid emulsion, allows to have the growth liquidsubstance in the form of a very thin film, coating minute bubbles of air(or other gas). The minute bubbles, colliding with the seeds or thegrowing granules inside the fluid bed, break and so the growth liquidfilm sticks on said particles, thereby obtaining a growth of the samethat is equivalent to the growth achieved with the prior art atomizeddroplets. Yet, that growth is obtained with a drastic reduction of thequantity (volumes) of the gaseous flow (air or other suitable gas) ascompared to the prior art, with a gas/growth liquid substance ratio evenreduced between 0.002 and 0.01 (i.e. 2-10 Kg of gas for 1000 Kg ofliquid substance).

Another important advantage is represented by the likewise drasticreduction in the supplying speed of said emulsion. The speed is nowdetermined by the liquid flow speed, typically between 2 and 60 m/s.

As an immediate consequence there is the concrete possibility to feedsuch emulsion to the fluid bed granulator with a very low speed comparedto what happens with the prior art atomizing nozzles. This carries thedouble advantage of lowering the consumption of energy and ofcontrolling the granule's growth inside the fluid bed, controlling, as aconsequence, the granulometry of the final product.

In fact, the low amounts of air (or other gas) requested for operatingthe nozzle, according to the present invention, allow to operate withinsignificant energy consumption if compared with the prior art, to thebenefit of the granule's production costs.

Furthermore, the low feeding speed allows to limit the final productgranulometry inside a predetermined range of values, which is muchnarrower if compared to the prior art. This because it is surprisinglypossible to control the seeds and granules whirling motion inside thefluid bed granulator, and therefore to control their growth.

The advantages and the features of the invention will be better shownfrom the description of an illustrative and non limiting embodiment ofthe invention, made hereinafter with reference to the enclosed drawings

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically and in longitudinal section a nozzle forgrowth liquid distributor devices in fluid bed granulators, according tothe present invention.

FIG. 2 shows schematically and in cross section a fluid bed granulationapparatus comprising the nozzle of FIG. 1, according to the presentinvention.

DETAILED DESCRIPTION

With reference to FIG. 1, with 1 a nozzle according to the presentinvention is globally indicated, which is particularly suitable forsupplying a chosen granule's growth liquid substance in fluid bedgranulators.

Said nozzle comprises a duct 2, preferably cylindrical, provided, at oneend, with an opening 3, for the inlet of a continuous flow of saidgrowth liquid and, at the other end, with a portion 4, conically taperedtowards an opening 5, for supplying said liquid substance.

At a predetermined distance from said liquid supplying opening 5, adistributor device 6 for an air or other gas flow A is mounted on theduct 2. The device 6 is in fluid communication with the inside of saidduct trough a plurality of openings 7 (for example holes or slits), madeout from the same duct wall and preferably oriented in radial direction.On the other side, said distributor device 6 is in communication, trougha duct 6 a, with a source of, for example, pressured air, which is notrepresented since conventional.

In a position between opening 3 and said distributor device 6, aswirling device 8 (of the type for example with fixed helical vanes) ismounted inside duct 2 as emulsifying means. Said swirling device is ableto set in helical motion a liquid flux F, fed axially in said duct 2through opening 3 with rectilinear feed motion.

A nozzle according to the present invention, during a fluid bedgranulation process, works as follows.

Two continuous flows are fed inside duct 2 at the same time: a granule'sgrowth liquid flow F, through opening 3, and an air flow A, through thedistributor's 6 plurality of openings 7.

As mentioned above, the air/growth liquid ratio may vary between 0.002and 0.01.

When traversing the swirling device, the substantially rectilinearliquid flux F is set in rotational motion, so that, downstream from saidswirling device 8, said flow's motion is helical. This helical motionhas axial feed speed substantially equal to that in the duct stretchdownstream from the swirling device 8 and a predetermined tangentialspeed such that a gas in liquid emulsion can be generated as describedhereinafter.

Depending on the granulation type to be obtained, the feed speed of thegrowth substance flow is for example comprised between 2 and 60 m/s,while the tangential speed is for example comprised between 2 and 30m/s.

And, downstream from the swirling device 8, at these predeterminedtangential speeds, the impact between the growth liquid flow and the airflow, continuously blown through the distributor 6, takes place. As aconsequence, the air is subjected to a very fast splitting in minutebubbles that, maintaining their individuality, penetrate through thegrowth liquid mass under the effect of centripetal forces due to saidtangential motion of the liquid mass. Essentially, the formation of anemulsion of air in said growth liquid substance takes place.

When considering urea granulation, it was for instance surprisinglynoted that with a feed speed of the growth liquid substance, comprisedbetween the above-mentioned values, 50-200 micron bubbles (air inliquid) were obtained; said bubbles were coated by a very thin film ofsaid liquid substance, with thickness comprised for example between 1and 10 micron.

In the portion of duct 2 comprised between where the emulsion is formedand the supplying opening 5, the bubble flow gradually gainscompactness, with bubbles uniformly spread in its cross-section and withfeed speed, for example, substantially equal to that of the liquid flowat the inlet in duct 2.

This flow of minute bubbles coated by the very thin growth liquid film,obtained with very small air consumption (as to what was until nowpossible for the same substance atomization), is supplied through theopening 5 in, for example, a fluid bed of growing seeds and granules,with a very reduced speed if compared to that currently set by the priorart.

With reference to FIG. 2, a fluid bed granulation apparatus (orgranulator) according to the present invention, globally indicated with9, is very schematically and partially represented.

In that figure, details structurally and functionally equivalent tothose represented in the previous figure will be indicated with the samereference numbers and will be no further described.

Granulation apparatus 9 comprises a container 10, wherein a fluid bed 11of seeds and granules of the chosen substance to be granulated isobtained, a device for feeding continuously said seeds in said fluid bed(duct 12), a fluidification and support system of the fluid bed(perforated bottom 13 and blowing means—not represented sinceconventional—of fluidification air or other gaseous fluid FL) and atleast a distributor device 14 for the granule's growth liquid flow F.The apparatus 9 is also provided of a device (duct 15) for the weirdischarge of the final product.

Advantageously, distributor device 14 includes one (as in the example ofFIG. 2) or more growth liquid supplying nozzles 1, of the described typewith reference to FIG. 1.

The invention thus conceived may be susceptible to variations andmodifications, all falling within the scope of protection defined in thefollowing claims.

For instance, instead of the swirling device 8, emulsifying means may beobtained by positioning the openings 7 as to the axis of duct 2 in asuitable manner (for example tangential to it), so to obtain atangential gaseous flow feeding with respect to the growth liquid flow.This tangential gaseous flow, supported by a predetermined feedingspeed, imparts said helical motion to the liquid flow.

According to a further embodiment of the present invention, the openings7 in FIG. 1, positioned in radial direction as regards the axis of duct2, can act as emulsifying means, should said gaseous flow be sentthrough said openings with suitable and predetermined feeding speed.

Furthermore, depending on the volume of air or other gas to be fed inthe liquid flow, duct 2 may have a sole opening 7, suitably dimensioned.

Finally, the portion 4 of duct 2 can be manufactured as substantiallyrectilinear or tapered toward the outside; so the swirling device 8 canbe of dynamic type, for example a turbine.

1. A nozzle for distributor devices for a granule growth liquidsubstance in fluid bed granulators, comprising: a duct having, at oneend, at least one inlet opening for a flow of a chosen granule's growthliquid substance, and, at the other end, a supply opening for saidsubstance; a gaseous flow distributor externally associated to said ductin predetermined spaced relationship from said supply opening and influid communication with the inside of said duct; and emulsifying meansassociated to said inlet opening and said distributor to obtain, insidea cylindrical portion of said duct, an emulsion of said gaseous flow insaid growth liquid substance.
 2. Nozzle according to claim 1, whereinsaid emulsifying means comprise a swirling device located inside saidduct between said at least one inlet opening and said distributor, saidswirling device being able to impart a helical motion to an axial flowof said growth liquid substance inside said duct.
 3. Nozzle according toclaim 1, wherein said gaseous flow distributor is in fluid communicationwith the inside of said duct through at least one opening in a wall ofsaid duct.
 4. Apparatus according to claim 1, wherein said gaseous flowdistributor is in fluid communication with the inside of said ductthrough at least one opening in a wall of said duct.
 5. A fluid bedgranulation apparatus, comprising: a container in which a fluid bed ofseeds and granules of a chosen substance to be granulated is obtained; adevice for feeding continuously said seeds in said fluid bed; afluidification and support system of the fluid bed; and at least onedistributor device for a flow of a granule growth liquid substance,wherein said distributor device comprises at least one supplying nozzlefor said granule growth liquid substance, comprising a duct having, atone end, at least one inlet opening for a flow of said liquid substance,and, at the other end, a supply opening for said substance, a gaseousflow distributor externally associated to said duct in predeterminedspaced relationship from said supply opening and in fluid communicationwith the inside of said duct, and emulsifying means associated to saidinlet opening and said gas flow distributor to obtain, inside acylindrical portion of said duct, an emulsion of said gaseous flow insaid growth liquid substance.
 6. Apparatus according to claim 5, whereinsaid emulsifying means comprise a swirling device located inside saidduct between said at least one inlet opening and said distributor, saidswirling device being able to impart a helical motion to an axial flowof said growth liquid substance inside said duct.